Voltage regulators find use in many applications, such as in the integrated circuits used in the automotive industry. For example, with reference to FIG. 1, a power supply system 100, used in an automotive integrated circuit, may comprise first and second regulators 102, 104, of which the first regulator 102 is coupled to a main domain 106, whereas the second regulator 104 is coupled to a back-up domain 108. Here, the first regulator 102 may be a high capacity regulator with a higher current consumption compared to the lower capacity second regulator 104. There are typically three operational modes of the system 100 as follows. In a run mode, the switch 110 is on, and both the first and the second regulators 102, 104 see an external capacitance 112, and both the main domain 106 and the back-up domain 108 are powered. In a standby mode, the first regulator 102 is switched off, with the switch 110 remaining on. As such, the second regulator 104 continues to see the external capacitance 112, i.e. the external capacitance remains charged. This enables changing of the operational mode from the standby to the run mode without significant charge-up delay.
In a back-up mode, again the first regulator 102 is switched off while the second regulator 104 remains on, but the switch 110 is in an off position. In this mode, the second regulator 104 no longer sees the external capacitance 112, and, with the first regulator 102 being switched off, the external load 112 will discharge. As a result, moving from the back-up mode to the run mode will have a charge-up delay.
In many applications, of which the system in FIG. 1 is only one example, there is a need to provide a regulator architecture that is stable for low as well as high capacitive loads.
FIG. 2 shows an open loop architecture 200 of a regulator with an nmos driver 202, which can provide a solution that is stable for both low and high capacitive loads. However, the architecture 200 can only function for a large drop out due to the Vgs required for the nmos driver 202. For example, for an output voltage Vout of 1.2 volt, Vgs may be of the order of 1.0V, thus requiring a supply voltage Vin of for example about 2.5V. Furthermore, because there is no feedback coming directly from Vout, Vout is not very well controlled, and use of a nmos driver also means that load regulation is poor.
A need therefore exists to provide a regulator structure that seeks to address one or more of the abovementioned problems.